The present invention relates to a clamp for a clamping device for a refractory plate in a seating of a slide valve in a casting installation, an assembly comprising a refractory plate and its seating, a slide valve incorporating such an assembly, a casting installation incorporating such a slide valve and a process for clamping a refractory plate.
It is known that the refractory plates used in slide valves in metallurgical casting installations are mounted in their seatings by clamping.
These seatings may take the form of fixed elements on the valve frame in the case of fixed plates, or carriages for the mobile plates of the slide valve.
Clamping is generally carried out by means of a clamp which, on one hand, bears against one edge of the plate and, on the other hand, against an adjustable stop which serves to press the clamp against the plate in order to immobilise it.
With known clamps, the plate is held in its seating in a satisfactory manner. However, a notable difficulty is posed by the variability in shape between plates, which may be due to the fabrication process or required for various reasons. This variability can give rise to imbalances in the bearing contact between the clamp and plate, resulting in the application of very high localised forces.
In the long term, these elevated stresses can damage both the clamp and the plate, which is already subject to cracking by virtue of its normal duty.
The present invention has the purpose notably of providing a clamp which does not have the shortcomings of known clamps.
The object of the present invention is a clamp for a clamping device for a refractory plate in a seating of a slide valve in a casting installation, the said clamp having on one hand a thrust zone whereon it can receive a clamping force tending to push the clamp against a refractory plate located in the seating and, on the other hand, two ends of which each is capable of being applied against one edge of the refractory plate, characterised in that the clamp is capable of being elastically deformed and in that each of the two ends of the clamp is also conformed such that it bears against an adjacent wall of the seating under the effect of a suitable clamping force (and greater than the force required to cause the clamp to bear solely on the edges of the plate), or under the effect of thermal expansion of the plate due to the high temperatures observed during casting operations, or under the combined effect of these two actions.
The document EP-A1-220,070 discloses a clamping mechanism for a plate into a support frame. This clamping mechanism includes a stirrup or U shaped clamp adapted to the peripheral profile of an end face of the refractory plate. The stirrup or U-shaped clamp has adjustment means and guides for adjustment parallel to the peripheral profile of the refractory plate. As the stirrup does not bear simultaneously on the refractory plate and on the support frame (FIG. 2), the clamping can only be assured by the clamp itself which has to be made of a rigid material. When, in use, the plate is brought to high temperature and expands, extremely high local stresses are generated in the plate since the stirrup or U shaped clamp is made of material which has no elasticity at all. On the other hand, if the plate is not immediately clamped, assuming there is a possibility to clamp the plate later while the plate is already in use and hot, there is a risk of movement of the plate in its support frame. Such a movement could be catastrophic for the safety and security of the personnel and installation.
One of the advantages of the clamp according to the invention is that it adapts automatically to the geometry of the plate which it is required to immobilise. Thus, variations in shape between plates due to the fabrication process do not cause any clamping problems. Similarly, the ability of the clamp to conform automatically to the bearing surfaces presented by the plate, by virtue of its elasticity, avoids the clamp itself being subjected to unduly high stresses and eventually breaking.
In this way, by virtue of its elasticity, the clamp according to the invention itself absorbs some of the deformation of the plate due to its expansion and then, during casting operations, transmits to the plate seating the clamping forces exerted by the adjustable stop and by the deformation due to expansion of the plate.
In other words, the clamp behaves like a self-positioning brace between the plate and its seating.
In regard to elastic deformation of the clamp, the following factors will be taken into account: advantageously, a clamp with a rigidity constant below 10 T/mm will be selected, preferably below 5 T/mm, and even more preferably in the order of 1 to 3 T/mm. These values may be compared with those measured on known clamps, which range from 10 to 30 T/mm, or even higher. Hitherto, it has always been considered that the clamp, when present, must have sufficient rigidity for the plate to be acted upon directly when the slide valve is set in motion, without allowing the slightest amount of play to develop. In this situation, it is necessary for the rigidity constant of the clamps in question to be at least greater than 10 T/mm, and generally greater than 20-30 T/mm.
Departing from known principles, the inventors opted for a considerably less rigid clamp whose elasticity absorbs some of the expansion of the plate without generating large stresses until the moment when the ends of the clamp come into contact with and bear against the walls of the seating (which generally have a rigidity constant greater than 40 T/mm, and even in the order of 150 to 200 T/mm in the case of certain ladle slide valves). The clamp then simply acts as a brace between the plate, which at this point has almost reached its maximum size, and the seating. As the plate has almost reached its maximum size when the ends of the clamp begin to bear against the walls of the seating, the stresses generated in the plate are very substantially reduced.
Advantageously, however, the clamp must not absorb all of the deformation due to thermal expansion of the plate so that the latter remains in compression during the casting operations. Indeed, it is beneficial for the plate to be maintained in compression so that any cracks which may develop are held closed.
Advantageously, the clamp is fabricated in one piece by machining, casting or forging in a material possessing the requisite properties having regard to the temperature conditions, mechanical strength and elasticity of the clamp. Examples of suitable materials for fabrication of the clamp according to the invention are all types of steel, in particular steel 42CrMo4.
In a particular embodiment, at least one of the two ends of the clamp is connected to the thrust zone by an elastically deformed portion of the clamp, allowing the orientation of the end to be changed.
This change of orientation allows the said end to bear against the plate over a surface contact thereby avoiding the application of punctual forces detrimental for the plate.
The second bearing surface, which is rounded, serves as a xe2x80x9cpivotxe2x80x9d allowing the contact made between the end of the clamp and the plate to impose the orientation of the said end, so that the contact thus made is a surface-type contact.
In a particular mode of implementation, the clamp includes only one thrust zone. The clamping force applied by an adjustable stop in the seating is thus automatically distributed between the two ends of the clamp thereby avoiding any imbalance between the clamping forces applied by the two ends of the clamp on the plate.
Preferably, the thrust zone presents a smooth surface (which may be flat or rounded) to make contact with the adjustable stop in the seating, which can apply its clamping force at any point on this smooth surface. In this way, the clamp is able to assume a balanced position between the seating and the clamp, possibly by deflecting away from the longitudinal axis of the seating by reason of asymmetry in the plate, without disturbing the bearing contact between the adjustable stop of the seating and the thrust zone.
In a particular mode of implementation, at least one of the ends of the clamp incorporates, in cross section, a cut-out enabling the said end to engage under a projection in the wall of the seating.
This projection serves to prevent the clamp from dropping out of the seating when the clamping force on the plate is released.
The object of the invention is also an assembly of a refractory plate and its seating, in the form of a carriage or a fixed element on the valve frame, incorporating a seating to accommodate the said refractory plate, characterised in that the refractory plate is held in the seating by means of a clamp as described above.
According to a particular mode of implementation of the invention, the carriage or fixed element of the valve frame is provided with a clamping arrangement to exert the clamping force on the clamp. This clamping arrangement consists of a screw, a cam, a thrust block or any other variant known to the person skilled in the art.
Advantageously, this clamping arrangement is removable so that, in case it becomes stuck in the clamped position, it can be readily detached from the assembly.
The invention also relates to a slide valve in a casting installation incorporating such an assembly, and to a casting installation.
The present invention also relates to a process for clamping a plate in a seating of a slide valve in a casting installation, comprising the step of placing a clamp between the plate and one edge of the seating, the said clamp having, on one hand, a thrust zone whereon a clamping force can be exerted so as to push the clamp against a plate located in the seating and, on the other hand, two ends of which each is capable of being applied against one side of the plate, characterised in that a clamping force is applied to the clamp causing it to deform elastically until each end of the clamp bears against the corresponding edge of the plate, preferably until the ends of the clamp are sufficiently close to the wall of the seating to be able to bear thereon when the plate expands under the effect of the temperature reached during casting.